1. Field of the Invention
The present invention relates generally to a cushioning mechanism to be incorporated in a chair which is typically employed in an office, and more particularly to a cushioning mechanism for use with the seat portion of such a chair and an interlocking cushioning mechanism which is arranged to cushion the seat portion and a backrest in an interlocked manner.
2. DESCRIPTION OF THE PRIOR ART
It is well known that a typical cushioning mechanism for use with the seat portion of an office chair may include a gas spring, a coil spring, a torsion bar or various other kinds of cushioning members.
In addition, various proposals have been made with respect to an interlocking cushioning mechanism which is arranged to cushion the seat portion and a backrest of such an office chair in an interlocked manner. Such an interlocking cushioning mechanism typically includes as the cushioning member for the seat portion a gas spring, a coil spring, a torsion bar or the like, such cushioning member being interlocked with the backrest via a link mechanism such as to cushion the swinging motion of the backrest. An interlocking cushioning mechanism of this type is disclosed, for example, in U.S. Pat. No. 4,533,177 and Japanese Patent Laid-open No. 29304/1986.
Also known is a cushioning mechanism of a spring type in which it is possible to adjust the degree of cushioning, for example, the hardness or resiliency of an incorporated spring. In such a conventional spring type cushioning mechanism, however, the mechanism becomes complicated and the number of parts used is also increased, resulting in an increase in its size. In other words, such a prior-art mechanism involves the problem of including a large number of potential failure factors.
In particular, adoption of the type in which a spring is incorporated in a leg or support frame or a seat frame has the tendency to result in a complicated structure.
A previously proposed type of cushioning mechanism which is so arranged as to interlock the seat portion and the backrest also requires a complicated interlocking mechanism. Another conventionally proposed type in which the degree of cushioning, for example, the hardness or resiliency of a spring, is adjustable requires a complicated mechanism and a large number of parts, and this leads to an increase in size. Such a type therefore involves the problem of including a large number of potential failure factors.